Implantable prostheses are commonly used to replace or augment body tissue. In the treatment of breast cancer, it is sometimes necessary to remove some or all of the mammary gland and surrounding tissue. Reconstruction of the breast commonly involves surgical implantation of a prosthesis which both supports surrounding tissue and restores the appearance of the breast. The restoration of the normal appearance of the body has an extremely beneficial psychological effect on post-operative patients, eliminating much of the shock and depression that often follows extensive surgical procedures. Implantable prostheses are also used more generally for restoring the normal appearance of soft tissue in various areas of the body, such as the buttocks, chin, calf, etc.
Soft implantable gel-filled prostheses typically include a flexible envelope or shell made of cured silicone-based elastomer encasing a silicone gel core. Obviously, a shell that is highly resistant to both rupture and the possibility of silicone gel bleeding through the shell is highly desirable. Breast implants have been designed with these goals in mind.
Conventional breast implant shells are multilayered or laminated. Specifically, such shells include outer “rupture-resistant” layers, and an inner “barrier” layer, sandwiched between the outer layers and effective to resist gel bleed. For example, some silicone-filled breast implants available from Allergan, Inc. include a low diffusion silicone elastomer shell made with outer layers of a dimethyl-diphenyl silicone elastomer, having a diphenyl polymer mole percent of 5%, and a barrier layer of dimethyl-diphenyl silicone elastomer having a diphenyl polymer mole percent of 15%.
Mentor Corp. manufactures gel-filled breast implants which include a layered silicone elastomer shell made with outer layers of a dimethyl silicone elastomer and an intermediate barrier layer of a dimethyl diphenyl silicone copolymer having a diphenyl polymer mole percentage of 15%.
One drawback of utilizing layered or laminated implant shells is that during formation of the shell, mixing of adjacent layers may result in visible clouding. Surgeons prefer a relatively transparent shell. Moreover, a shell having a layered construction presents the potential problem of delamination.
Despite many advances in the construction of soft prosthetic implant shells, there remains a need for a more flexible gel-filled prosthesis which minimizes gel bleed.